qapi: Implement deprecated-input=reject for QMP command arguments

This policy rejects deprecated input, and thus permits "testing the
future".  Implement it for QMP command arguments: reject commands with
deprecated ones.  Example: when QEMU is run with -compat
deprecated-input=reject, then

    {"execute": "eject", "arguments": {"device": "cd"}}

fails like this

    {"error": {"class": "GenericError", "desc": "Deprecated parameter 'device' disabled by policy"}}

When the deprecated parameter is removed, the error will change to

    {"error": {"class": "GenericError", "desc": "Parameter 'device' is unexpected"}}

Signed-off-by: Markus Armbruster <armbru@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Message-Id: <20210318155519.1224118-11-armbru@redhat.com>

include/qapi/compat-policy.h

@@ -17,6 +17,15 @@
 
 extern CompatPolicy compat_policy;
 
+/*
+ * Create a QObject input visitor for @obj for use with QMP
+ *
+ * This is like qobject_input_visitor_new(), except it obeys the
+ * policy for handling deprecated management interfaces set with
+ * -compat.
+ */
+Visitor *qobject_input_visitor_new_qmp(QObject *obj);
+
 /*
  * Create a QObject output visitor for @obj for use with QMP
  *

include/qapi/qobject-input-visitor.h

@@ -15,6 +15,7 @@
 #ifndef QOBJECT_INPUT_VISITOR_H
 #define QOBJECT_INPUT_VISITOR_H
 
+#include "qapi/qapi-types-compat.h"
 #include "qapi/visitor.h"
 
 typedef struct QObjectInputVisitor QObjectInputVisitor;
@@ -58,6 +59,9 @@ typedef struct QObjectInputVisitor QObjectInputVisitor;
  */
 Visitor *qobject_input_visitor_new(QObject *obj);
 
+void qobject_input_visitor_set_policy(Visitor *v,
+                                      CompatPolicyInput deprecated);
+
 /*
  * Create a QObject input visitor for @obj for use with keyval_parse()
  *

include/qapi/visitor-impl.h

@@ -113,6 +113,9 @@ struct Visitor
        The core takes care of the return type in the public interface. */
     void (*optional)(Visitor *v, const char *name, bool *present);
 
+    /* Optional */
+    bool (*deprecated_accept)(Visitor *v, const char *name, Error **errp);
+
     /* Optional */
     bool (*deprecated)(Visitor *v, const char *name);
 

include/qapi/visitor.h

@@ -459,6 +459,15 @@ void visit_end_alternate(Visitor *v, void **obj);
  */
 bool visit_optional(Visitor *v, const char *name, bool *present);
 
+/*
+ * Should we reject deprecated member @name?
+ *
+ * @name must not be NULL.  This function is only useful between
+ * visit_start_struct() and visit_end_struct(), since only objects
+ * have deprecated members.
+ */
+bool visit_deprecated_accept(Visitor *v, const char *name, Error **errp);
+
 /*
  * Should we visit deprecated member @name?
  *

qapi/qapi-visit-core.c

@@ -135,6 +135,15 @@ bool visit_optional(Visitor *v, const char *name, bool *present)
     return *present;
 }
 
+bool visit_deprecated_accept(Visitor *v, const char *name, Error **errp)
+{
+    trace_visit_deprecated_accept(v, name);
+    if (v->deprecated_accept) {
+        return v->deprecated_accept(v, name, errp);
+    }
+    return true;
+}
+
 bool visit_deprecated(Visitor *v, const char *name)
 {
     trace_visit_deprecated(v, name);

qapi/qmp-dispatch.c

@@ -19,6 +19,7 @@
 #include "qapi/qmp/dispatch.h"
 #include "qapi/qmp/qdict.h"
 #include "qapi/qmp/qjson.h"
+#include "qapi/qobject-input-visitor.h"
 #include "qapi/qobject-output-visitor.h"
 #include "sysemu/runstate.h"
 #include "qapi/qmp/qbool.h"
@@ -27,6 +28,14 @@
 
 CompatPolicy compat_policy;
 
+Visitor *qobject_input_visitor_new_qmp(QObject *obj)
+{
+    Visitor *v = qobject_input_visitor_new(obj);
+
+    qobject_input_visitor_set_policy(v, compat_policy.deprecated_input);
+    return v;
+}
+
 Visitor *qobject_output_visitor_new_qmp(QObject **result)
 {
     Visitor *v = qobject_output_visitor_new(result);

qapi/qobject-input-visitor.c

@@ -14,6 +14,7 @@
 
 #include "qemu/osdep.h"
 #include <math.h>
+#include "qapi/compat-policy.h"
 #include "qapi/error.h"
 #include "qapi/qobject-input-visitor.h"
 #include "qapi/visitor-impl.h"
@@ -43,6 +44,7 @@ typedef struct StackObject {
 
 struct QObjectInputVisitor {
     Visitor visitor;
+    CompatPolicyInput deprecated_policy;
 
     /* Root of visit at visitor creation. */
     QObject *root;
@@ -662,6 +664,23 @@ static void qobject_input_optional(Visitor *v, const char *name, bool *present)
     *present = true;
 }
 
+static bool qobject_input_deprecated_accept(Visitor *v, const char *name,
+                                            Error **errp)
+{
+    QObjectInputVisitor *qiv = to_qiv(v);
+
+    switch (qiv->deprecated_policy) {
+    case COMPAT_POLICY_INPUT_ACCEPT:
+        return true;
+    case COMPAT_POLICY_INPUT_REJECT:
+        error_setg(errp, "Deprecated parameter '%s' disabled by policy",
+                   name);
+        return false;
+    default:
+        abort();
+    }
+}
+
 static void qobject_input_free(Visitor *v)
 {
     QObjectInputVisitor *qiv = to_qiv(v);
@@ -696,6 +715,7 @@ static QObjectInputVisitor *qobject_input_visitor_base_new(QObject *obj)
     v->visitor.end_list = qobject_input_end_list;
     v->visitor.start_alternate = qobject_input_start_alternate;
     v->visitor.optional = qobject_input_optional;
+    v->visitor.deprecated_accept = qobject_input_deprecated_accept;
     v->visitor.free = qobject_input_free;
 
     v->root = qobject_ref(obj);
@@ -718,6 +738,14 @@ Visitor *qobject_input_visitor_new(QObject *obj)
     return &v->visitor;
 }
 
+void qobject_input_visitor_set_policy(Visitor *v,
+                                       CompatPolicyInput deprecated)
+{
+    QObjectInputVisitor *qiv = to_qiv(v);
+
+    qiv->deprecated_policy = deprecated;
+}
+
 Visitor *qobject_input_visitor_new_keyval(QObject *obj)
 {
     QObjectInputVisitor *v = qobject_input_visitor_base_new(obj);

qapi/trace-events

@@ -17,6 +17,7 @@ visit_start_alternate(void *v, const char *name, void *obj, size_t size) "v=%p n
 visit_end_alternate(void *v, void *obj) "v=%p obj=%p"
 
 visit_optional(void *v, const char *name, bool *present) "v=%p name=%s present=%p"
+visit_deprecated_accept(void *v, const char *name) "v=%p name=%s"
 visit_deprecated(void *v, const char *name) "v=%p name=%s"
 
 visit_type_enum(void *v, const char *name, int *obj) "v=%p name=%s obj=%p"

scripts/qapi/commands.py

@@ -154,7 +154,7 @@ def gen_marshal(name: str,
 
     ret += mcgen('''
 
-    v = qobject_input_visitor_new(QOBJECT(args));
+    v = qobject_input_visitor_new_qmp(QOBJECT(args));
     if (!visit_start_struct(v, NULL, NULL, 0, errp)) {
         goto out;
     }
@@ -258,7 +258,6 @@ def _begin_user_module(self, name: str) -> None:
 #include "qapi/compat-policy.h"
 #include "qapi/visitor.h"
 #include "qapi/qmp/qdict.h"
-#include "qapi/qobject-input-visitor.h"
 #include "qapi/dealloc-visitor.h"
 #include "qapi/error.h"
 #include "%(visit)s.h"

scripts/qapi/visit.py

@@ -87,6 +87,9 @@ def gen_visit_object_members(name: str,
             indent.increase()
         if deprecated:
             ret += mcgen('''
+    if (!visit_deprecated_accept(v, "%(name)s", errp)) {
+        return false;
+    }
     if (visit_deprecated(v, "%(name)s")) {
 ''',
                          name=memb.name)

tests/unit/test-qmp-cmds.c

@@ -303,6 +303,29 @@ static void test_dispatch_cmd_deprecated(void)
     do_qmp_dispatch_error(false, ERROR_CLASS_COMMAND_NOT_FOUND, cmd);
 }
 
+static void test_dispatch_cmd_arg_deprecated(void)
+{
+    const char *cmd = "{ 'execute': 'test-features0',"
+        " 'arguments': { 'fs1': { 'foo': 42 } } }";
+    QDict *ret;
+
+    memset(&compat_policy, 0, sizeof(compat_policy));
+
+    /* accept */
+    ret = qobject_to(QDict, do_qmp_dispatch(false, cmd));
+    assert(ret && qdict_size(ret) == 1);
+    qobject_unref(ret);
+
+    compat_policy.has_deprecated_input = true;
+    compat_policy.deprecated_input = COMPAT_POLICY_INPUT_ACCEPT;
+    ret = qobject_to(QDict, do_qmp_dispatch(false, cmd));
+    assert(ret && qdict_size(ret) == 1);
+    qobject_unref(ret);
+
+    compat_policy.deprecated_input = COMPAT_POLICY_INPUT_REJECT;
+    do_qmp_dispatch_error(false, ERROR_CLASS_GENERIC_ERROR, cmd);
+}
+
 static void test_dispatch_cmd_ret_deprecated(void)
 {
     const char *cmd = "{ 'execute': 'test-features0' }";
@@ -403,6 +426,8 @@ int main(int argc, char **argv)
                     test_dispatch_cmd_success_response);
     g_test_add_func("/qmp/dispatch_cmd_deprecated",
                     test_dispatch_cmd_deprecated);
+    g_test_add_func("/qmp/dispatch_cmd_arg_deprecated",
+                    test_dispatch_cmd_arg_deprecated);
     g_test_add_func("/qmp/dispatch_cmd_ret_deprecated",
                     test_dispatch_cmd_ret_deprecated);
     g_test_add_func("/qmp/dealloc_types", test_dealloc_types);